Selective termination of superhydrophobic surfaces

ABSTRACT

Provided herein is a hierarchical superhydrophobic surface comprising an array of first geometrical features disposed on a substrate comprising a first material, and an array of second geometrical features disposed on the first features to form a hierarchical structure and a terminal level disposed on the second features, wherein the terminal level comprises a second material, the second material being different from the first material. The second material has a hydrophilicity different from the hydrophilicity of at least one of 1) the hydrophilicity of the second material and 2) hydrophilicity induced by the hierarchical structure. The present disclosure further methods of preparing hierarchical superhydrophobic surfaces and medical devices comprising the hierarchical superhydrophobic surfaces.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims benefit of U.S. Provisional Application No.62/460,568 filed on Feb. 18, 2017, which is hereby incorporated byreference in its entirety.

TECHNICAL FIELD

The present disclosure provides a hierarchical superhydrophobic surface,wherein a metastable Cassie-Wenzel wetting state forms when the surfaceis in contact with a wet surface. The present surfaces are resistant tostructural degradation and reduction of tissue localization propertieswhen used as a medical implant.

BACKGROUND

Tissue adherent implants are known that use a Cassie-Wenzel state tolocalize the implant. Such implants comprise a substrate onto which atleast two geometric surface patterns are disposed. A hierarchicalsurface is a surface with geometrical features that can be grouped bysize and those features are stacked.

A hydrophilic surface makes a contact angle with a drop of pure waterthat is less than 90 degrees. A superhydrophobic surface is a surfacethat has a contact angle with water of greater than 140 degrees. Thenotion of hydrophilicity has a kinetic interpretation as well. Accordingto the Washburn model, hydrophilicity is related to the filling rate ofcapillaries. For example, a filling rate of about 2 mm/min for a glasscapillary with an inner diameter of 5 nm corresponds to a contact angleof 80 degrees.

Hydrophilicity is also associated with surface energy. Generally, highsurface energy corresponds to a hydrophilic surface, and low surfaceenergy corresponds to a hydrophobic surface. Surface energy is a complexcombination of the chemistry and the geometry of a surface.

There are four generally recognized wetting states: 1) Wenzel, 2) Cassieor Cassie-Baxter, 3) Wenzel-Cassie, and 4) hemi-wicking. A hierarchicalsurface may comprise any combination of these wetting states. Consider asurface comprising a substrate having a first level A and a terminallevel B, and a drop of water that covers a region C of the substrate.Not all of the substrate in region C need be in contact with the water.A Wenzel state is a wetting state in which pure water contacts theentire surface of both levels A and B, and thus covers the entiresurface of the substrate in the region C. A Cassie state is a wettingstate in which the water is in contact with Level B only. Finally, aWenzel-Cassie state is a wetting state in which the water is in contactwith one level and only partially in contact with another level in theregion C. A hemi-wicking state is any of the above three wetting statesin which the water contacts a region outside of the region C.

A Wenzel wetting state is one which interacts with a wet surfaceinitially by attracting water to the substrate, followed by watersaturation and then vanishing of the attraction. A Cassie wetting stateis one which interacts with a wet surface by repelling water from it. AWenzel-Cassie wetting state both attracts and repels water on a wetsurface, and consequently cannot be saturated without applyingcompression energy. Consequently, a hemi-wicking Wenzel-Cassie statewould be particularly useful in surfaces that contacts living tissue.

All of these wetting states result from a complex interaction of thedipole nature of water with the dipole nature of the substrate and aninteraction between the surface tension of water and the geometry of thesubstrate surface. In completely liquid environments, such as thosefound in the human body, water surface tension can result from waterlocalized on hydrophilic regions of a substrate interacting with lipidslocalized on lipophilic regions of a substrate. Accordingly, while thefour above identified wetting states traditionally are defined in agas-water-solid system, analogous wetting states are obtained in alipid-water-solid system. In most cases, hydrophobic regions on ahierarchical surface correspond to lipophilic regions when placed in aliving body.

There is a need for superhydrophobic hierarchical contact surfaces thatare useful particularly for medical implants and other contactindications. Such surfaces would provide appropriate tissue adherence.Furthermore, there is a need for superhydrophobic hierarchical surfaceshaving improved mechanical features such that they do not containgeometrical features that are subject to distortion or fouling. Thepresent disclosure addresses these needs.

BRIEF SUMMARY

The present disclosure generally relates to a hierarchicalsuperhydrophobic surface comprising an array of first geometricalfeatures disposed on a substrate comprising a first material, and anarray of second geometrical features disposed on the first features toform a hierarchical structure and a terminal level disposed on thesecond features, wherein the terminal level comprises a second material,the second material being different from the first material.

It has been surprisingly discovered that a hierarchical superhydrophobicsurface in which the terminal level has been replaced by a smoothhydrophilic substance displays a Wenzel-Cassie behavior, incontradiction with classical wetting models. Indeed, substitution ofgeometrically induced hydrophilicity with chemical hydrophilicity, andsubstitution of a geometrically induced hydrophobicity with chemicalhydrophobicity, can be applied at any level of the hierarchical surface.For example, a smooth hydrophobic hierarchical substrate coated inregions with a smooth hydrophilic substance can act as pinning sites forWenzel-Cassie states.

Generally, the present hierarchical surfaces provide novel wettingstates that result from localized variation in surface energy resultingfrom combinations of chemical surface energy and geometrical surfaceenergy. In addition to providing novel wetting states, in considerationof the unexpected observation above, terminal level geometricalfeatures, which may be susceptible to mechanical distortion or foulingmay be beneficially replaced with a terminal smooth substance. Forexample, a terminal pattern level formed by the geometrical features maybe replaced. While not being bound by theory, it is understood that itis the differences in surface energy in regions and their relative sizesthat creates the wetting states of the present disclosure. Accordingly,in some cases a hydrophobic level A terminated with a hydrophilicsubstance behaves similarly to a hydrophilic level A terminated with ahydrophobic substance.

In one or more embodiments, at least one of the first geometricalfeatures, second geometrical features or terminal level is modified toenhance fixity between the hierarchical structure and a living tissue.In one or more embodiments, a functional coating is disposed on at leasta portion of the hierarchical structure.

In one or more embodiments, the hierarchical structure is characterizedby a specific surface area of at least about 100 times the specificsurface area of a flat solid substrate of the same dimensions.

In one or more embodiments, the solid substrate of the hierarchicalstructure is compact or porous.

In one or more embodiments, the substrate is inorganic or organic. Inone or more embodiments, the substrate comprises polylactic acid,polyurethane, polypropylene, silicone, or combinations thereof.

In one or more embodiments, the geometrical surfaces comprise pillars,two-dimensional sinusoids, triangular prisms, flutes or combinationsthereof. In one or more embodiments, the pillars are cylindricalstructures with diameters ranging from about 1 to about 10 microns atone level and from 10 to 30 microns at another level, and aspect ratiosranging from about 1 to about 10.

In one or more embodiments, the terminal level comprises a hydrophilicsolid. In one or more embodiments, the terminal level comprises ahydrophobic solid.

In one or more embodiments, the hierarchical surface is disposed on orformed as a part of a medical device or implant. The surfaceadvantageously affixes the device or implant to tissue in vivo.

In one or more embodiments the terminal level is functionalized by amethod selected from the group (a) solution chemistry, (b) chemicalvapor deposition, (c) plasma deposition, (d) atomic layer deposition,(e) physical vapor deposition, or a combination thereof.

A superhydrophobic hierarchical surface can be subjected tosolution-based chemistry near the geometric feature with a fluid. Incertain embodiments, the coating chemistry includes precipitationreactions, but, other processes are also possible, such as molecularadsorption, colloidal deposition, polymerization, and catalyticreactions.

In one embodiment, solid precipitates are grown from solution byheterogeneous nucleation onto the exposed geometric features of thesurface.

In one aspect, a method of localized formation of a material includescontacting a superhydrophobic hierarchical surface comprisinggeometrical features with a non-wetting fluid comprising a material tobe locally formed on features or a precursor thereto, where thesuperhydrophobic surface and the fluid are selected such that the fluidwets only an upper portion of the geometrical features; and causing thematerial to form on the features. In one or more embodiments, theterminal level comprises micro-scale or nano-scale pillars, or theterminal level can comprise a random array of isolated or interconnectedgeometrical features.

In one or more embodiments, the terminal level is chemically treated toinclude either a hydrophobic coating or a hydrophilic coating.

In one or more embodiments, the terminal level is treated to providebonding or adherent interaction of the coating material and the terminalsurface. For example, the terminal level may selectively be treated withionizing radiation.

In one or more embodiments, the coating material comprises molecules,polymers, colloidal particles, or mixtures thereof. In some embodiments,the material is catalytic, magnetic, optically-active, piezoelectric orbioactive.

In another aspect, a method of localized formation of a coating materialincludes providing a superhydrophobic hierarchical surface comprisinghierarchical geometric features with said features comprising at leasttwo regions having different surface properties, contacting the surfacewith a fluid, said liquid comprising a material to be locally formed onthe geometrical features, or a precursor thereof, wherein the surfaceproperties of the two or more geometrical features and the fluid areselected such that the fluid wets one or the other or both of the atleast two regions, and causing the material to selectively deposit atone or the other or both of the at least two regions.

In one or more embodiments, the method further includes contacting thecoated geometrical features with a second fluid, said second fluidcomprising a second material to be locally deposited, or a precursorthereof, wherein the material is deposited over both the first andsecond regions.

In one or more embodiments, the superhydrophobic hierarchical surfacecomprises pillars, two-dimensional sinusoids, and flutes, or the surfacecomprises an array of silicon or polymeric pillars, or the surfacecomprises a random array of geometric features. In one or moreembodiments, the geometric features are chemically treated to provide ahydrophobic layer, a hydrophilic layer, or a tissue bonding or tissueadherent layer.

In one or more embodiments, the adherent material is catalytic,magnetic, piezoelectric or bioactive. In other embodiments, the adherentmaterial comprises organic or inorganic precipitates, molecules,polymers, colloidal particles, or mixtures thereof.

In one or more embodiments, the tissue bonding material is adherent toan uppermost portion of the terminal level.

In one or more embodiments, the geometrical features comprise at leasttwo regions having different surface properties, and the adherentmaterial is adherent to at least one of said two regions.

The present disclosure further provides methods of producing theaforementioned hierarchical superhydrophobic surfaces comprising:providing an array of a first geometrical feature disposed on asubstrate, and a second geometrical feature disposed on the firstfeature to form a hierarchical structure, and forming the terminal levelby a method selected from solution chemistry, chemical vapor deposition,plasma deposition, atomic layer deposition, physical vapor deposition,or a combination thereof.

The present disclosure further provides a medical device comprising theaforementioned hierarchical superhydrophobic surfaces.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1A depicts a hierarchical superhydrophobic surface comprisingarrays of hierarchically disposed geometric surface features. FIG. 1Bdepicts the surface of FIG. 1A, in which a second material has beendeposited on the terminal features.

FIG. 2 depicts a schematic of nucleation precipitation on the tips of ahierarchical surface.

FIG. 3 depicts a hierarchical superhydrophobic surface of the presentdisclosure in which several functional layers are provided at theterminal level and on other geometrical on the surface.

FIG. 4 is a schematic illustrating a precipitate writing process usefulfor functionalizing geometric surface features of the presentdisclosure.

FIG. 5A depicts a perspective view of a hierarchical superhydrophobicsurface according to the present disclosure. FIG. 5B is a top view ofthe array. FIG. 5C is an expanded perspective view of the hierarchicalsuperhydrophobic surface, and FIG. 5D is a further expanded perspectiveview of the hierarchical superhydrophobic surface.

FIGS. 6A and 6B depict an embodiment of a hierarchical superhydrophobicsurface according to the present disclosure in which the firstgeometrical surface is a sinusoidal pattern.

FIGS. 7A and 7B depict an expanded side view of two embodiments of ahierarchical superhydrophobic surface in which the first geometricalstructure is a sinusoidal pattern.

DETAILED DESCRIPTION

The following description is an exemplification of the principles of thepresent disclosure and is not intended to limit the disclosure to theparticular embodiments illustrated herein.

The present disclosure provides, in some embodiments, a hierarchicalsuperhydrophobic surface comprising an array of first geometricalfeatures disposed on a substrate comprising a first material, and anarray of second geometrical features disposed on the first features toform a hierarchical structure and a terminal level disposed on thesecond features, wherein the terminal level comprises a second material,the second material being different from the first material.

In particular embodiments, the second material has a hydrophilicity thatdiffers from the hydrophilicity of the first material. In otherembodiments, the second material has a hydrophilicity that differs fromthe hydrophilicity induced by the hierarchical structure of the surface.

The geometric features of the present disclosure may have any shape. Forexample, the features may be pillars (such as cylindrical pillars),sinusoids, triangular prisms, flutes, ridges, squares, rectangles, ovalsand the like. In a particular embodiment, the geometrical features arepillars. In other embodiments, the features are a combination of pillarsand sinusoids. In a particular embodiment, the substrate comprises asinusoidal shape, and the first and second geometric features comprisepillars. The terminal level may further comprise pillars having adifferent material from the substrate and first and second pillars. In afurther embodiment, the second set of pillars further comprises flutesor ridges disposed along a vertical axis of the pillar.

In certain embodiments, at least one of the geometric features can becoated with a hydrophobic or hydrophilic material.

In some embodiments, the terminal level comprises a smooth functionalcoating, such as a smooth tissue attractive coating.

In certain embodiments, the second material disposed on the terminallevel is bonded or adherent to the terminal level via van der Waalsinteraction, covalent interaction, ionic interaction, hydrogen bonding,or combinations thereof.

In certain embodiments, the terminal level comprises a smooth functionalcoating. The functional coating may be a tissue attractive coating.

In some embodiments, the first geometrical features comprise a width ordiameter ranging from about 1 micron to about 100 microns, preferablyabout 10 microns to about 50 microns, and the second geometricalfeatures have a width ranging from about 100 nm to about 10 microns,preferably about 1 micron to about 10 microns.

In some embodiments, the first and second geometrical features have anaspect ratio ranging from about 1 to about 10.

In some embodiments, the first geometrical features have a pitch rangingfrom about 10 to about 1000 microns, about 10 to about 500 microns,about 50 to about 100 microns or about 100 to about 1000 microns. Thesecond geometric features may have a pitch ranging from about 10 nm toabout 100 microns, about 1 micron to about 100 microns, about 1 micronto about 50 microns or about 10 micron to about 50 microns.

In some embodiments, the first material comprises polylactic acid,polyurethane, polypropylene, silicone or a combination thereof. Incertain embodiments, the second material comprises polylactic acid,polyurethane, polypropylene, silicone or a combination thereof, providedthat the second material is different from the first material.

A superhydrophobic surface is a surface with at least a portion of itssurface making a contact angle with water greater than 140 degrees. Ahierarchical surface is a surface with geometrical features that can begrouped by size and those features are stacked. For example, a surfacemay have one set of features characteristically of sizes between 100 nmand 1 micron, and another set of features characteristically of sizesbetween 5 microns and 10 microns, wherein substantially all of thefeatures on a surface can be placed in either group, with very fewfeatures in the size ranges of 1 micron to 5 microns, <100 nm, and >10microns. Each of the characteristic size ranges are called levels. Thelevel corresponding to the smallest characteristic size is called theterminal level.

A surface comprised of levels A and B where the size of A is greaterthan the size of B, then the surface is said to be arrangedhierarchically if the features of B are on top of the features of A.Examples are 1) small pillars arranged on the flat top of largerpillars, 2) flutes or ridges on the sides of pillars, and 3) pillarsarranged on a surface resembling a two-dimensional sinusoid.

Hydrophilicity can result from the chemical structure of a material, orthe surface geometry of a material. When the surface geometry changesthe hydrophilicity of the substrate, then the changed hydrophilicity iscalled an induced hydrophilicity. Chemically hydrophilic materials canbe made more hydrophobic with the addition of surface texture, andchemically hydrophobic materials can be made more hydrophilic with theaddition of a surface texture. A material that comprises most of thesurface area of a hierarchical surface is called a substrate.

A superhydrophobic surface is metastable if portions of the surface wetor attract water and other portions of the surface resist wetting orrepel water. Hierarchical surface patterns are generally responsible formetastability, where the hydrophilicity at each level is different.Generally, there is at least one level that is hydrophilic and at leastone other level that is hydrophobic.

The notion of hydrophilicity has a kinetic interpretation as well.According to the Washburn model, hydrophilicity is related to thefilling rate of capillaries. For example, a filling rate of about 2mm/min for a glass capillary with an inner diameter of 5 nm correspondsto a contact angle of 80 degrees.

Hydrophilicity is also associated with surface energy. Generally, highsurface energy corresponds to a hydrophilic surface, and low surfaceenergy corresponds to hydrophobicity. Surface energy is a complexcombination of the chemistry and the geometry of a surface.

There are four generally recognized wetting states: 1) Wenzel, 2) Cassieor Cassie-Baxter, 3) Wenzel-Cassie, and 4) hemi-wicking. A hierarchicalsurface may comprise any combination of these wetting states. Consider asurface comprising a substrate having a first level A and a terminallevel B, and a drop of water that covers a region C of the substrate.Not all of the substrate in region C need be in contact with the water.A Wenzel state is a wetting state in which pure water contacts theentire surface of both levels A and B, and thus covers the entiresurface of the substrate in the region C. A Cassie state is a wettingstate in which the water is in contact with Level B only. Finally, aWenzel-Cassie state is a wetting state in which the water is in contactwith one level and only partially in contact with another level in theregion C. A hemi-wicking state is any of the above three wetting statesin which the water contacts a region outside of the region C.

A Wenzel wetting state is one which interacts with a wet surfaceinitially by attracting water to the substrate, followed by watersaturation and then vanishing of the attraction. A Cassie wetting stateis one which interacts with a wet surface by repelling water from it. AWenzel-Cassie wetting state both attracts and repels water on a wetsurface, and consequently cannot be saturated without applyingcompression energy. Consequently, a hemi-wicking Wenzel-Cassie state isparticularly useful in surfaces that contacts living tissue. Ahemi-wicking Wenzel-Cassie state resists saturation (maintains grip)even in the presence of water-eluting living tissue. For example, thesurfaces of the present disclosure are usefully hemi-wicking and canmaintain adherence to a melting ice cube, even at angles as great at 90degrees to the horizon. Accordingly, the surfaces of the presentdisclosure typically comprise 3 or more levels, wherein the first levelis hemi-wicking, the second level is hydrophilic or hydrophobic, and thethird level is more hydrophilic or hydrophobic than the second layer.

All of these wetting states result from a complex interaction of thedipole nature of water with the dipole nature of the substrate and aninteraction between the surface tension of water and the geometry of thesubstrate surface. In completely liquid environments, such as thosefound in the human body, water surface tension can result from waterlocalized on hydrophilic regions of a substrate interacting with lipidslocalized on lipophilic regions of a substrate. Accordingly, while thefour above identified wetting states traditionally are defined in agas-water-solid system, analogous wetting states are obtained in alipid-water-solid system. In most cases, hydrophobic regions on ahierarchical surface correspond to lipophilic regions when placed in aliving body. A Wenzel-Cassie state between a hierarchicalsuperhydrophobic surface and living tissue is referred to as tissuebonding hydrophobicity.

One of the functional components used in the present surfaces may behydrophobic, and may contain a fluorine-containing moiety whichassociates with gas phase oxygen or alternatively associates withlipophilic substances. The second functional component may behydrophilic, and when implanted readily associates with water. Uponimplantation, the two functional components set up domains ofhydrophobic constituents derived from the implant environment anddomains of hydrophilic constituents derived from the implantenvironment. The structure is selected such that the implant derivedhydrophobic constituents bead or possess high surface tensionjuxtaposing the regions of implant derived hydrophilic constituents. Thedegree to which the implant derived constituents fill the geometry ofthe surface determines whether a Cassie or wettable Cassie state existslocally. Depending on the time and conditions surrounding the implant,either the aqueous or lipo fractions may be, relatively, more spreading.Therefore, the implant surface may be simultaneously adhesive tohydrophobic substances and repulsive to hydrophilic substances, or viceversa, and this condition may be designed to change with time.

The following definitions apply to the present disclosure. A hydrophilicsurface is a surface that makes a contact angle with a drop of purewater that is less than 90 degrees. A surface A is said to be morehydrophilic than another surface B if the contact angle for A is lessthan the contact angle for B. Hydrophobicity is the inverse ofhydrophilicity. When the water drop is substituted with an oil drop,then the corresponding terms are lipophilic and lipophobic.

Referring to FIG. 1A, a hierarchical superhydrophobic surface 100 can becontacted with a fluid 110 containing a material to be locally depositedat the terminal level of the surface to obtain low contact angles. Incertain embodiments, the surface without the local deposition ofmaterial forms water contact angles greater than or equal to 140degrees. Hierarchical superhydrophobic surfaces have geometric featuresthat are typically on the order of microns or nanometers in at least onedimension. The surface structures can be an ordered or disordered arrayof protrusions stacked hierarchically.

Any superhydrophobic surface may be used, including electrospun polymerarrays, ordered arrays of pillars, a suitably randomly rough surface, alayer of spheres, lines, and the like which are chemically hydrophobicor are geometrically hydrophobic.

In some embodiments, the superhydrophobic surface can include nano andmicro surface structures that result in a high degree of surfaceroughness that is hemi-wicking, such as relatively large amplitude (100to 1000 microns) two-dimensional sinusoids. High amplitude surfaceroughness can substantially increase the tissue fixing propensity of thehierarchical superhydrophobic surfaces by preventing fluid saturation ofthe surface, and thereby cause the phenomenon of tissue bondingsuperhydrophobicity.

The spacing, height and other dimensions of the features on thegeometric features are matters of discretion. For example, thedimensions of the structures may be on the order of angstroms,nanometers, or microns.

These structures can be fabricated from any biocompatible polymer,preferably with relatively low bending modulus, for example, silicone,polyurethane, polypropylene, polylactic acid, or an organic polymer.Exemplary superhydrophobic surfaces can include arrays of organicmicro-pillars, such as polylactic acid micro-pillars that are obtainedfrom a negative mold formed by etching the surface of a silicon wafer.Other biocompatible hydrophobic materials for use in the presentsurfaces include fluorinated polymers, e.g., PTFE and hydrophobicsilanes.

The present surfaces are advantageously treated to enhance tissuebonding hydrophobic properties of the surface. For example, a lowsurface energy material can be deposited on the geometrical features toincrease the in vivo Cassie-Wenzel nature of the features. Conversely, ahigh surface energy material can be deposited on geometrical features toincrease the in vivo Cassie-Wenzel nature of the features.

In certain embodiments, the shape of the micro-pillars can providegreater flexibility in obtaining the desired tissue bondingsuperhydrophobic surfaces. As one particular non-limiting illustrativeexample of a hierarchical superhydrophobic surfaces, hydrophobic pillarswith a flared end on top of which is deposited a hydrophilic mediumuniquely sustains a Cassie-Wenzel state in vivo by preventing saturationwetting even for liquids that have a relatively low surface contactangle, such as angles between 40° and 90°.

Terminal Level Functionalization

The hierarchical superhydrophobic surfaces of the present disclosureinclude those that can be terminally functionalized by any suitableand/or desirable means. For example, the desired regions near the tipsof the superhydrophobic surface can be functionalized with any desiredgroups, such as groups that are capable of electrostatic, covalent,hydrogen bonding, and/or van der Waals interactions.

In one embodiment, surface structures having a terminal fine structurecan be functionalized by adhesion with surface groups that replace thefine structure with a smooth surface with a specific chemicalhydrophilicity, thus replacing geometric hydrophilicity with chemicalhydrophilicity.

In certain embodiments, the geometric features of the hierarchicalsuperhydrophobic surfaces can be functionalized in a variety of ways toprovide a surface for precipitation, adsorption or deposition ofmaterial from solution to occur. In one embodiment, a geometric featurecan be treated to deposit a layer of gold, which can then be reactedwith a variety of materials, e.g., hydrophobic thiol compound, to form ahydrophobic surface. Exemplary thiolated molecules includepoly(styrene-co-2,3,4,5,6-pentafluorostyrene-SH), poly(methylmethacrylate-co-pentafluorooctyl methacrylate-SH), but in general anyfluorinated or methylated thiol can be utilized. The tips of thegeometric feature can be further selectively functionalized bycontacting the thiol-treated surface with a solution that containsanother compound having the desired surface properties. Some exemplarymolecules include carboxylic acid-terminated thiols, sulfonated thiolmolecules, hydroxyl-terminated thiols, PEG-terminated thiols, and thelike.

While not being bound by theory, it is believed that geometricallyhydrophilic terminal structures can be locally replaced by chemicallyhydrophilic smooth surfaces. Doing so makes the present surfaces moremechanically robust by elimination of small scale features that may notreproduce well or degrade with use.

In another embodiment, a hydrophobic layer can be deposited on thesurface of the geometric features. For example, if the surface substrateis made of silicone, then the surface can be functionalized with afluorinated silane. The tips of the geometric features can be furtherselectively functionalized by contacting the hydrophobic surface with asolution that contains a tissue attractive component (e.g., oxides ofdextran). By controlling the superhydrophobic character of the surfaceand/or the fluid, the fluid can wet only desired regions of the tips andselectively functionalize the exposed tips of the surface. Exemplarymolecules include carboxylic acid terminated silanes, sulfonatedsilanes, hydroxyl-terminated silanes, PEG-terminated silanes.

The geometric features can be also functionalized using a microcontactapproach, by gently applying a roller to the tips of the nanostructuredsurface. In another approach, the hierarchical surfaces can be placedtop-side down on a surface coated with a functionalizing moiety, and thefunctionalizing moiety deposited on the terminal level by a variety ofmeans. For example, the deposition means may include polymerization,evaporative casting, UV-curing, or any method generally known tochemistry that induces a phase transition from a liquid state to a solidstate.

In some embodiments, the superhydrophobic surface can be selectivelyfunctionalized at any region along a dimension, e.g., the length, of thegeometric feature. For example, by controlling the interaction of thefluid to the superhydrophobic surface, a first fluid that contacts theterminal level of the superhydrophobic surface can be introduced. Thefirst fluid can contain desired materials which can adhere to theterminal level of the superhydrophobic surface and provide desired firstfunctional groups. A second fluid which penetrates to a deeper levelthan the first fluid into the superhydrophobic surface can be introducedto the superhydrophobic surface. The second fluid can contain desiredmaterials which can adhere below the terminal level or deeper on thelevel adjacent to the terminal level and provide desired secondfunctional groups. A third fluid which penetrates even deeper than thesecond fluid into the superhydrophobic surface can be introduced to thesuperhydrophobic surface. The third fluid can contain desired materialswhich can adhere below the second functional group and provide desiredthird functional groups. Alternatively, the three fluids can selectivelyadhere to discrete levels.

In some embodiments, the terminal level comprises three differentstructures all of approximately the same spatial dimension. Accordingly,the superhydrophobic surface has three different functionalities nearthe tip of the superhydrophobic surface. The structures may differ bytheir pitch, geometric form, or aspect ratio. This approach can beimplemented as desired to provide any number of desired functionalgroups near the tip of the superhydrophobic surface. As an alternativeembodiment to achieve the linear sequence of deposition of differentmaterials, an array of nanowires can be first covered completely with alayer of sacrificial material (e.g., polymer). Then the polymer layercan be etched away to reveal the tips of the posts that are thenfunctionalized as described above (either using the layer of gold whichis then functionalized with a thiol or, in case of Si structures, usingthe appropriate silane solution). The polymer layer can then bepartially etched further to reveal the next band on the wire, which isfunctionalized as described above. The process can be repeated toproduce the desired number of functionalized bands. At the end, theremaining layer of the sacrificial material can be etched and the bottomof the nanowires can be rendered hydrophobic. Suitable polymers may bechosen from those known in the art that are susceptible to etching, suchas, photoresist or polystyrene.

Terminal Level Substitution

In another embodiment, the geometric features can be functionalizedusing stepwise fabrication techniques. By way of example, the spacesbetween features can be filled with a sacrificial material, which canthen be selectively removed to expose the distal ends of the structure.The exposed ends can be functionalized, for example, using any of themethods and solutions described above, and the remaining sacrificialmaterial can be removed. The remainder of the superhydrophobic surfacecan be treated to apply a hydrophobic coating.

A hierarchical mould-based dewetting process may be used to isolate theterminal level from the other levels of the surface. The first stepcomprises placing a UV-curable hydrophobic polymer resin, for exampleperfluoropolyether, confined to be between a lower MHSS and a flat uppersheet made of a hydrophilic polymer resin, for example, polyurethaneacrylate. The second step comprises UV-curing the hydrophobic polymerresin and subsequently pulling back the flat upper sheet, exposing theterminal level of the MHSS without residual layer of hydrophobic polymerresin. A unique feature of this method is the capability of excluding aresidual layer at the terminal level by exploiting a high wettabilitydifference between and taking advantage of the hierarchical structure ofthe hierarchical superhydrophobic surface. The third step comprisesapplying the terminal substance, replacing the hydrophilic sheet,applying pressure, and allowing the applied substance to cure by solventdiffusion or some other method known in the art. In this instance, noresidual layer of terminal substance remains anywhere outside the locusof the terminal level. The fourth step comprises peeling back thehydrophilic cover sheet, and then peeling away the UV-cured hydrophobiclayer, leaving a hierarchical superhydrophobic surface with a terminallayer coated with a terminal substance. When the UV-curable resin isdropwise placed on the surface and covered by the hydrophilic sheet, theresin spontaneously spreads inside the confined spaces and a majority ofthe resin is squeezed out of the assembly on an application of pressureand due to the large affinity difference (dewetting) between the surfaceand UV-curable resin.

Precipitate Nucleation

Useful embodiments of terminal level deposition by precipitation areprovided. In some embodiments, the precipitate or deposited growths aredesigned to remain adherent to the tips of the surface structure. Insome embodiments, the method is used to provide adherent deposition andgrowth of material on the terminal level. The method can be used toincorporate useful materials onto a terminal level micro-pillar array,such as crystalline materials, especially materials with a largeelectric dipole or magnetic dipole moment. Still other materials includespin gel materials with anti-reactive oxygen species properties thatcould alter or inhibit the formation of ingrowth tissue, e.g., tissueadhesions.

Referring to FIG. 1A, which depicts a side view of a superhydrophobicsurface 100, an array of micro pillars 120 are disposed vertically onsubstrate 130. Substrate 130 can, in some embodiments be a medicaldevice or implant, such as an anti-adhesive sheet. A second level arrayof micropillars 122 are disposed vertically on the first pillars 120. Athird set of structures, which may be micro or nanopillars or wires 124is disposed on the second level pillars 122. A fluid 110 to be depositedon the terminal level can be a supersaturated solution with a solubleform of the material to be deposited or a precursor thereof, or asuspension of colloidal particles. As shown in FIG. 1B, deposition fromfluid 110 provides a terminal level 126 having a different chemicalcomposition from the substrate material. Terminal level 126 can be arough disordered surface, while in other embodiment 126 may be a smoothsurface. Nucleation deposition methods known in the art includedeposition through a temperature- or evaporation-induced solubilitychange, an insoluble reaction product, the addition of a common ion, orintroduction of an immiscible solvent, polymerization, addition ofreactive agents to liquid, exposing liquid to gas or vapor reagents thatinduce precipitation, reaction to an insoluble product, and the like.

The solution 110, e.g., an aqueous solution, can be in contact inlimited regions of the surface, where the superhydrophobicity of theterminal level can interact with the fluid in a manner to minimizesurface contact. Accordingly, the terminal pillars 124 provide sites fornucleation deposition of desired material. The point contacts of thesurface with the fluid can act as nucleation sites and/or sites forother chemical processes that are involved in the deposition process.For example, if the conditions are suitable for heterogeneousnucleation, then precipitation can occur in a controlled, localizedmanner only on those exposed tips. The superhydrophobic terminal levelcould further be chemically functionalized, to influence the precipitategrowth. For example, the superhydrophobic surface can be treated toincrease its hydrophobicity, to increase adherent interactions, e.g.,covalent or ionic interactions, with the deposited material and/or todirect deposition to occur at selected locations and/or in a selectedorder. In some embodiments, if the non-wetting solution is removed bywicking or evaporation, the desired localized precipitates can remain onthe terminal levels.

FIG. 2 provides a schematic illustration of a method for nucleationprecipitation on the tips of geometric features such as pillars,pyramids, fibers and the like. In FIG. 2, geometric feature 220comprises a second features 222 disposed thereon, such that 222 is theterminal level of the superhydrophobic surface. A third feature 224 isdisposed on feature 222. These features may be, in some embodiments,pillars. Nucleation 228 can begin from a supersaturated solution 210that contacts the exposed terminal level. Over time, the adherent growthof precipitates 228 can increase the size of the deposited material onand between the micro-pillars 224. The localized precipitate depositsremain on the micro-pillars 224 of the terminal level, both duringgrowth and following removal of the functional solution.

One exemplary way that such adherent deposition can be achieved is bythe chemical functionalization of the tips of the terminal levelstructures with functional groups that provide strong association withthe deposited material. Functional groups can improve adherence by avariety of physical phenomena, including electrostatic, van der Waals,hydrogen bonding, and/or covalent forces. The functionalizedmicro-pillars with adherent deposited material can interact with livingtissue to reduce Cassie-Wenzel saturation and increase the strength andduration of superhydrophobic tissue bonding.

Many different applications utilizing the structure formed in FIG. 2 canbe envisioned. For example, localized nucleation and growth of anadherent particle can be used to deposit a material 228 that is, forexample, hydrophilic, hydrophobic or tissue adherent, on a micro-pillarterminal level 224. In the case of a hydrophilic termination, when asurface is placed in contact with tissue, the functionalizedmicro-pillars 228 of the terminal level create pinning centers in aWenzel wetting state and the first level 220 creates a Cassie wettingstate. As a result the tissue is fixed in shear relative to thehierarchical superhydrophobic surface.

As another non-limiting example of different applications that can beenvisioned, adherent deposition of materials can occur at differentlocations on the levels of the surface in coordination with the locationand nature of the chemical functionality on the structure and theposition of the tissue interface. Chemical functionality can be used tocontrol the propagation and selection of cells across the tissueinterface. The selective surface functionalization of the levels of thehierarchical superhydrophobic surface makes it possible to control thespeed and type of cells that are adherent and can propagate across thesurface.

For example, a hierarchical superhydrophobic surface formed from abiocompatible polymer such as polyurethane can be functionalized withone or more functional groups. As noted above, functional groups canchange the surface properties of the terminal level of the hierarchicalsuperhydrophobic surface relative to the rest of the surface, and can,for example, improve the cell adherent properties of the functionalizedregion. In some embodiments, the various levels can be selectivelysurface functionalized using two or more functional groups. For example,a hierarchical structure of a first level of pillars with a terminallevel of pillars on the ends of the first level pillars can be coated atthe terminal level that completely encapsulates the terminal levelpillars and a second functional coating selectively coats the sides ofthe first level pillars.

FIG. 3 is a side view of a hierarchical superhydrophobic surface 300comprising geometrical features having multiple levels functionalized.The geometrical features in some embodiments are pillars. The surfacecomprises a base level 320 having a second geometric feature 322disposed thereon. A third feature 324 is disposed on the second featureproviding the terminal level. The top area of terminal level 324comprises a functionalized layer 310 comprising a first functional groupF1, a second functionalization layer 312 comprising a second functionalgroup F2 coats the walls of third level features 324 having functionalgroup F2, and a third functionalization layer 316 having functionalgroup F3 coating the hemi-wetting two-dimensional base level 320. As aresult of this functionalization, selective cellular growth can beachieved at the various levels of hierarchical superhydrophobic surface.

To achieve the multiple level deposition of materials as shown in FIG.3, a solution can be provided that contains several components, each ofwhich selectively deposits on individual specific levels. Alternatively,the materials can be deposited by exposing the surface to a series ofsolutions, each of which is selected to deposit a specific compound at aspecific location. The subsequently deposited materials do not depositon top of the previously deposited material(s). SURFACE TREATEDELECTROWRITTEN SUPERHYDROPHOBIC ADHERENT FIBERS

An embodiment of a hierarchical superhydrophobic surface comprising amatrix of electrowritten fibers 400 is depicted in FIG. 4.Electrowritten fibers are disposed on a base layer. A non-wettingdroplet of a functional solution, e.g., supersaturated solution of thecompound to be deposited or a precursor thereof, can be fed by asyringe, pipette, syringe pump or other delivery device and can belinearly translated across the electrowritten surface in a precipitatewriting process. As a result, a pattern of localized precipitatedeposits, molecules or colloidal particles can be produced on a fibrousmatrix. The delivery device can be in communication with a reservoir offunctional solution (not shown) and so can continually replenish thegrowth solution as deposition is ongoing. At the leading contact edge,the solution can contact the terminal level of surface (e.g. nanofibers)and nucleation can be initiated. As the droplet of solution is drawnover the surface, additional material can be deposited from solution andthe precipitates can grow. If the material, structure and growthconditions are such that the deposition is adherent, the depositedmaterials can remain on the substrate as the droplet continues totraverse the substrate. The deposits can remain on the terminal level.As a result, deposited material can be localized to the terminal levelof the surface.

Surface Pretreatments

Pretreatments comprise different processes that functionalize thesurface of the geometric features, such as oxygen plasma, gold coating,and self-assembled monolayer attachment. For example, non-water basedliquids or liquids having low surface tension (e.g., ethanol) can beused as a suitable solvent to introduce thiolated molecules to theterminal level of a surface. Such processes are expected to coat alongthe entire surface of the texture features; however, thesuperhydrophobic nature of the structure is expected to prevent completewetting when later exposed to a growth solution (e.g., a water-basedgrowth solution). For example, a negatively charged superhydrophobicsurface created by exposure to thiol can then interact with, forexample, positively charged particles to form particles attached ontothe superhydrophobic surface.

Examples of surface groups that can provide positive charges includeamine groups, which could be achieved using alkanethiol self-assembledmonolayer species such as ammonium salts, including but not limited toHS(CH₂)₁₁NH₃ ⁺Cl⁻, HS(CH₂)₁₁NMe₃ ⁺Br⁻, or HS(CH₂)₁₁C(NH₂)²+Cl⁻, or fromcolloidal particles having amine groups, such as polystyrene particlessynthesized with amidine surface groups.

Examples of surface groups that can provide negative charges includecarboxylic acid (—COOH), phosphate (—PO₃H₂), or sulfate (—SO₃) whichcould be achieved using alkanethiol self-assembled monolayers such asHS(C)nCOOH, HS(C)nSH, or HS(C)nP or having a silica surface having amultitude of silanol (Si—OH) groups which can become negatively-chargedover a range of pH.

Hydrogen bonding can be involved with strongly interacting chargedgroups such as amine (—NH₂) and —OH groups.

Covalent bonding can be achieved through the reaction between carboxylicacid (—COOH) with an amine group (—NH₂). Such types of covalent bondingreactions are involved in protein binding interactions.

Electrostatic attraction could also be achieved by applying a potentialto a conductive superhydrophobic surface, for the electrophoreticattachment of oppositely-charged particles. For example, the attachmentof negatively charged particles (such as SiO2 particles in basicconditions, or polystyrene particles with sulfate groups) onto a pillarstructure with a positive charge from an applied potential.

As noted above, the interaction between the particles and thesuperhydrophobic surface need not be limited to electrostaticinteractions as exemplified above. Other suitable interactions caninclude any surface chemistries one of ordinary skill in the art wouldreadily recognize.

FIG. 5 depicts several view of an exemplary hierarchicalsuperhydrophobic surface 500 of the present disclosure. FIG. 5A is aperspective view depicting the surface 500. Substrate 530 forms a baselevel upon which first geometric features 520 are disposed. Additionalgeometric features of the surface are not depicted in FIGS. 5 A and Bfor simplicity. As seen in FIG. 5B, which is a top view of the surface500, geometric features 520 may be ordered as depicted or disordered.The substrate 530 can form a medical device or implant, such as animplantable sheet, or may provide a surface for any other medicaldevice, such as a stent, retractor, prosthetic, and the like. FIG. 5C isa slightly expanded perspective view of the surface 500, depicting asecond set of geometric features 522 disposed on top of features 520 toproduce the hierarchical surface. Features 522 may be arranged in anordered fashion as shown or in a disordered fashion. FIG. 5D depicts afurther expanded perspective view depicting terminal level 540 disposedon the tips of second features 522. Terminal level 540 comprises amaterial having a different hydrophilicity from the substrate materialwhich forms the base layer 530 and features 520 and 522. For example,terminal level 540 may be more hydrophilic than the substrate materialor less hydrophilic than the substrate material. Although features 520and 522 are depicted as pillars, the present surfaces are not so limitedand it will be readily understood that the geometric features maycomprise pillars, sinusoids, triangular prisms, squares, rectangles,ovals, flutes or combinations thereof.

FIG. 6 depicts another embodiment in which the surface 600 comprises asinusoidal substrate layer 630. FIG. 6A shows a perspective view of anexemplary sinusoidal pattern having sinusoidal peaks 620 disposedthereon. The further geometric features and terminal layer are not shownin FIGS. 6A and 6B for simplicity.

FIGS. 7A and 7B depict a side view of a sinusoidal surface comprisingsubstrate 730 having peaks 720. Further geometrical features 722 aredisposed thereon, and terminal level 740 is disposed on features 722.Terminal level 740 comprises a material having a hydrophilicitydifferent from the substrate material 730 that forms the substrate andfeatures 720 and 722. Features 722 may, in some embodiments furtherinclude flutes or ridges 745. In FIG. 7A, the substrate 730 comprises asmooth bottom surface. In FIG. 7B, substrate 730 is a thin film having atop surface 760 and a complimentary shaped bottom surface 750.

Example 1: Nucleation of CaCO3 Particles

A surface of pillars on top of pillars was prepared from non-crosslinkedpolyurethane by solvent casting on a silicon inverse mold of the desiredsurface structure. The terminal level, due to its higher pillar densitywill be more hydrophilic than the larger pillar structure. Accordinglythe terminal level will preferentially attract ionic solutions. A 50 mMaqueous solutions of ionic CaCl2 was prepared from CaCl2 (Sigma-Aldrich)in distilled water. The CaCl2 solution is lightly and uniformly coatedon a flat hydrophilic surface. The surface is placed terminal level downon the surface, whereby the CaCl2 selectively adheres to the terminallevel. The CaCl2, residing on the surface was then placed in a chamberand exposed to a flow of carbon dioxide gas from a nitrogen gas flowover ammonium carbonate powder ((NH4)2CO3, Sigma-Aldrich). After about30 minutes, the droplets were removed from the substrate by evaporation,and the substrates removed from the chamber. The result is amonodisperse array of CaCO3 particles filling the terminal level of thesurface.

Example 2: Nucleation of Fe3O4 Particles

A surface of pillars on top of pillars was prepared from non-crosslinkedpolyurethane by solvent casting on a silicone inverse mold of thedesired hierarchical superhydrophobic surface. The terminal level, dueto its higher pillar density will be more hydrophilic than the largerpillar structure. Accordingly the terminal level will preferentiallyattract ionic solutions. An aqueous solution of ionic FeCl2 was preparedfrom FeCl2 (Sigma-Aldrich) in distilled water. The FeCl2 solution islightly and uniformly coated on a flat hydrophilic surface. Thehierarchical surface is placed terminal level down on the surface,whereby the FeCl2 selectively adheres to the terminal level. Theprepared hierarchical surface was exposed to an atmosphere of NH3 usingammonia solution in a closed chamber. The ammonia caused theprecipitation of Fe3O4. After about 10 minutes, the droplet was removedto leave behind the deposit of Fe3O4 nanoparticles encasing the terminallevel.

Example: Terminal Level Substitution of Polyurethane

An hierarchical surface formed from a mold comprised of a first leveltwo-dimensional sinusoid, a second level pillar array, and a terminallevel pillar array, and the terminal level pillar array includes flutesevenly spaced circumferentially on the external walls of the terminallevel pillars. The surface comprises polylactic acid. The hierarchicalsuperhydrophobic surface was placed in a tray with the first level downand anchored to the bottom of the tray. Then the tray was filled to alevel coincident with the tops of the level two pillars and allowed tocure. A solution of polyurethane was prepared by dissolving 10% w/wpolyurethane in acetone. The solution was poured over the siliconelayer, and a flat sheet of silicone placed on top. The acetone diffusesinto the silicone and precipitates the polyurethane on the terminallevel selectively. The top layer of silicone is removed. Theinterstitial layer of silicone is removed, leaving a polylactic acidhierarchical superhydrophobic surface having a terminal levelfunctionalized with polyurethane.

Shear Test of Hierarchical Superhydrophobic Surfaces

Hierarchical superhydrophobic surfaces comprising of pillars on top ofpillars were prepared and tested for shear properties when placedagainst beef steak. The test articles were hierarchical surfaces aloneand surfaces with the terminal level functionalization. Polyurethane(AP1780), polylactic acid (PLA) and Silicone were the test materials.All results are given in lbs/cm2 units. Each surface was tested fivetimes.

TABLE 1 Shear test Test Article Shear Force lbs/cm² Hierarchical surfacewithout terminal level modification AP1780 0.046 +/− 0.007 PLA 0.059 +/−0.005 Hierarchical surface with terminal level modification AP1780 withPLA terminal level 0.031 +/− 0.004 PLA with AP1780 f terminal level0.068 +/− 0.006 PLA with silicone terminal level 0.043 +/− 0.004

APPLICATIONS

A wide range of materials can be locally deposited by exposing theterminal level of geometric features to a liquid layer. For example, asuitable liquid can include a range of organic and inorganic compoundsthat can be deposited from solution. The solution can be aqueous,anhydrous, or lipophilic. The terminal level structures can serve as adeposition and/or a growth site. For example, the terminal levelstructures can serve as nucleation sites for deposition, as aheterogeneous catalyst for the nucleation and precipitation of thematerial, or as an adsorption site for the adsorption of molecules on asurface. In other embodiments, the fluid can contain a colloidalsuspension of particles that can be deposited on the wetted surfaces ofthe terminal level, through covalent or non-covalent attachment.

In still other embodiments, the solution treatment can include a firstprecursor solution to prepare the terminal level for a second solutionof deposition material that reacts to form an adherent solid phase. Thereaction can include nucleation that results in deposition on theexposed surfaces of the terminal level. For example, the solution cancontain a monomer, which is polymerized in the fluid and which isdeposited as a polymer on the exposed terminal surfaces of the geometricfeature. Alternatively, the deposition fluid can contain a componentwhich reacts to a precursor deposit on the terminal surface of thegeometric features when subjected to a suitable reagent or catalyst.

A variety of useful materials can be grown from solution onto theterminal level of hierarchical superhydrophobic surface, to create newstructures with chemical or geometrical functionality. For example, abioactive or catalytic compound could be grown on the terminal level ofthe hierarchical superhydrophobic surface, providing an array ofcatalytic or bioactive dots, e.g., adhesive points. The depositedmaterial can be adherent and, as such, can serve as a substrate forfurther processes, including cell adhesion, protein adsorption,angiogenesis, bacteriostasis, nitric oxide release, and antioxidation.

The above non-limiting exemplary applications make apparent to one ofordinary skill in the art numerous other applications that can beenvisioned with the hierarchical superhydrophobic surface surfaces ofthe present disclosure.

The description provided herein is not to be limited in scope by thespecific embodiments described, which are intended as singleillustrations of individual aspects of certain embodiments. The methods,compositions and devices described herein can comprise any featuredescribed herein either alone or in combination with any otherfeature(s) described herein. Indeed, various modifications, in additionto those shown and described herein, will become apparent to thoseskilled in the art from the foregoing description and accompanyingdrawings using no more than routine experimentation. Such modificationsand equivalents are intended to fall within the scope of the appendedclaims.

All publications, patents and patent applications mentioned in thisspecification are herein incorporated by reference in their entiretyinto the specification to the same extent as if each individualpublication, patent or patent application was specifically andindividually indicated to be incorporated herein by reference. Citationor discussion of a reference herein shall not be construed as anadmission that such is prior art.

Thus, although there have been described particular embodiments of thepresent disclosure of hierarchical superhydrophobic surfaces it is notintended that such references be construed as limitations upon the scopeof this disclosure except as set forth in the following claims.

What is claimed is:
 1. A hierarchical superhydrophobic surfacecomprising a substrate having superhydrophobicity wherein thesuperhydrophobicity is generated from a hierarchical microstructure, thehierarchical microstructure including an array of first geometricalfeatures disposed on the substrate, the array of first geometricalfeatures having a pitch between adjacent features from 10 to 1000microns, an array of second geometrical features disposed on the firstgeometrical features, the array of second geometrical features having apitch between adjacent features from 10 to 50 microns, and a terminallevel disposed on the second geometrical features, wherein the terminallevel is a chemical coating comprising a hydrophobic thiol compound; andwherein the hierarchical microstructure is configured to generate aWenzel-Cassie state for adhering the substrate to a target surface. 2.The hierarchical superhydrophobic surface of claim 1, wherein the firstand second geometrical features are selected from the group consistingof pillars, sinusoids, triangular prisms, flutes, ridges, squares,rectangles, ovals, and combinations thereof.
 3. The hierarchicalsuperhydrophobic surface of claim 1, wherein the array of firstgeometrical features is a two-dimensional sinusoid and the array ofsecond geometrical features is pillars.
 4. The hierarchicalsuperhydrophobic surface of claim 1, wherein the array of first, second,or both geometrical features is ordered.
 5. The hierarchicalsuperhydrophobic surface of claim 1, wherein the array of first, second,or both geometrical features is disordered.
 6. The hierarchicalsuperhydrophobic surface of claim 1, wherein the chemical coating of theterminal level comprises a functional coating that attracts smoothtissue to contact the functional coating.
 7. The hierarchicalsuperhydrophobic surface of claim 1, wherein the chemical coating isbonded or adherent to the second geometrical features via van der Waalsinteraction, covalent interaction, ionic interaction, hydrogen bonding,or combinations thereof.
 8. The hierarchical superhydrophobic surface ofclaim 1, wherein the first geometrical features comprise a width ordiameter ranging from about 1 micron to about 100 microns, and thesecond geometrical features have a width ranging from about 100 nm toabout 10 microns.
 9. The hierarchical superhydrophobic surface of claim1, wherein the first and second geometrical features have an aspectratio ranging from about 1 to about
 10. 10. The hierarchicalsuperhydrophobic surface of claim 1, wherein the surface has a surfacearea of at least 100 times the surface area of a surface having the samedimensions but without the hierarchical microstructure.
 11. Thehierarchical superhydrophobic surface of claim 1, wherein the substratecomprises polylactic acid, polyurethane, polypropylene, silicone or acombination thereof.
 12. The hierarchical superhydrophobic surface ofclaim 1, wherein the hydrophobic thiol compound is selected frompoly(styrene-co-2,3,4,5,6-pentafluorostyrene-SH) or poly(methylmethacrylate-co-pentafluorooctyl methacrylate-SH).